VoiceOfEnki explained it above. You need to study the site more though.
What's happening "in the head of a fantasist" is real though. Thoughts are real. Thoughts create reality. Even the things in your mind are real and create reality. Dreams are real. Dreams happen in a higher plane that exists, the mental plane which is above the astral plane. Every thought, especially a focused one creates a thoughtform that exists as a being of itself in the mental plane.
A mental plane experience (like a dream or a thought) is as real as a physical plane experience. The idea that your mind is separate from reality came in the 17th century and is false.
I mean, you keep asking these question that assume the materialistic worldview. If you want to really understand things, you need to change your worldview and view everything as real. I gave you a couple of books in your other thread that explain this, read them or at least study similar material on the web before asking anything else.
You also need to try and experience things for yourself.
No, you are wrong about dreams.
Dreams are not a higher dimensional thing than the Astral. It is the opposite.
The realm of the mind has various layers as well. At the highest layers, consciousness can be higher than the Astral, but this is not the realm of human consciousness.
Dreams in a human mind can be understood as a bubble that is contained inside your own self. They exist in the realm of inner consciousness, which is contained inside yourself, not outside in the existing reality. Even inside your own inner world, the dreams make up only a small finite bubble compared to the infinite microcosm within the self.
Dreams aren't real either. They are ephemeral things, not of substance. The Astral is real, existing, has substance, has continuity, exists outside of the self and on top of the Universe.
The personal realm of dreams is very small, like a miniature world inside the mind of an individual.
Compared to the greater reality, how small is the individual? The same is true for dreams. They are miniscule, very tiny projections of the individual mind about facets of reality that you know or have interacted with or have imagined about. Dreams are nothing special in the grand reality and existence of All.